Canopy Cover Gradient Research Articles

Spatial variation in current and historical management of Arabica coffee across forests in its indigenous distribution

Societal Impact StatementArabica coffee grows in the forests and woodlands of Ethiopia. These Arabica coffee populations contain a reservoir of the highest genetic variation of this species, which is extremely valuable from a biodiversity conservation and coffee breeding point of view. Knowledge about the distribution of these populations, including how and to what extent they have been managed by local communities now and in the past, is limited. We reveal insights into the history, distribution, and management of Arabica coffee populations in the remaining forests of Ethiopia, which is essential for developing effective conservation policies for this globally important resource.Summary To guide conservation of forest biodiversity in a broad sense, we need to understand the landscape‐level variation in current and historical management practices of agroforestry systems. We collected data on coffee management practices across a large forested landscape in Ethiopia within Arabica coffee's indigenous distribution, using interviews in 11 villages and field surveys and interviews at 78 coffee sites in the forest. There was a gradient in coffee density (higher), liana cover (lower), and canopy cover (lower) from sites with high management intensity to sites without management. Recently, management intensity has increased in the forest edges. Interviews suggest that substantial areas of currently unmanaged coffee forests are a legacy of reforestation of abandoned (semi‐) open landscapes in the late 19th century. Despite a dynamic history of coffee cultivation across these areas, the conservation of forest biodiversity, including unmanaged populations of genetically diverse Arabica coffee, should be a priority, given the few such remaining areas in Ethiopia and elsewhere in the world.

The role of sheltered habitats in biodiversity conservation of species sensitive to drought: a case study using ground beetles (Coleoptera, Carabidae) in the Gorongosa National Park

In the aftermath of 2019’ tropical cyclones Idai and Kenneth, we assessed ground beetle communities of the Gorongosa National Park (GNP) in Mozambique. The influence of habitat shelters, namely the buffering role of closed microhabitat conditions on Alpha diversity and community trait values during a long period of drought, was evaluated across the main habitat types of the park: miombo forests, mixed forests, transitional forests, and grasslands (open savannas). These habitat types comprised a distance gradient in relation to lake Urema, in the center of GNP. Miombo forests were farther from the lake while grasslands and transitional forests were in the floodplain area. Ground beetle communities were sampled using pitfall traps set up at 25 sites of each habitat type along an environmental gradient of tree canopy cover during the last twenty days of the dry season. Higher species richness of ground beetles was found in closed habitat shelters along the distance gradient to lake Urema. A higher functional diversity was also found along the canopy gradient, with larger sized and wingless species being more abundant in closed habitats than in open areas. This result highlights the crucial role of habitat closedness in the protection of sensitive ground beetles. In particular, the buffer effect of tree canopy and the protection of the understory plants and the litter layer was critical for the survival of hygrophilous species and will be key in conservation strategies to face climate aridification and habitat fragmentation.

Residual canopy cover provides buffering of near-surface temperatures, but benefits are limited under extreme conditions

Increasing summer temperatures and higher probabilities of extreme heat events have led to concerns about tree damage and mortality. However, insufficient attention has been given to conditions leading to heat-related regeneration failures in temperate forests. To address this, managers need to understand how microclimate varies under a range of overstory conditions. We measured air temperatures at 2 cm above-ground underneath a gradient of canopy cover on south-facing slopes in recently thinned Douglas-fir stands in western Oregon, USA. To expand the ecological relevance of these data to impacts on regeneration, we created the stress degree hours (SDH) metric, representing the amount of time—and by how much—temperatures exceeded biologically relevant stress thresholds. Overall, for every 10% increase in canopy cover, maximum temperatures at 2 cm were 1.3 °C lower, the odds of temperatures exceeding stress thresholds for conifer regeneration declined by a multiplicative factor of 0.26, and the total of SDH decreased by 40%. These reductions are large enough to be worthy of attention when managing for tree regeneration. However, data collected during the Pacific Northwest Heat Dome in June 2021 indicate that with various climate change scenarios and heatwave occurrences, temperatures will be unfavorable for regeneration regardless of overstory cover.

Land use/land cover change and carbon footprint in tropical ecosystems in Benin, West Africa

Extensive research has explored land use and land cover change (LULCC) in tropical ecosystems, but more detailed carbon footprint data is essential for defining strategies to enhance carbon sinks. This study assessed LULCC and its associated carbon footprints in different natural ecosystems. It also established forest reference levels (FRL). We used Landsat images for supervised classification and conducted forest inventories in 186 plots that span moist semi-deciduous forest, swamp forest, gallery forest, woodland and savannah areas. Biomass calculations employed allometric models, biomass expansion factors, and root-to-shoot ratios. Except in Lama Forest Reserve, anthropogenic pressures led to the regressive conversion of natural forest areas to savannah, croplands, and fallows. A progressive trend was observed in semi-deciduous forest (3.18 % per year), resulting in a positive LULC carbon footprint (16.06 tCO2eq.yr−1ha−1). 41.94 % of typical swamp forest was lost, releasing -62.89 tCO2eq.yr−1ha−1. Similarly, woodland decreased by -1.48 and -5.89 % per year, according to considered site, with emissions of -12.16 and -21.83 tCO2eq.yr−1ha−1, respectively. FRL followed the gradient of canopy cover of the different vegetation types. The results highlight the need for adequate conservation and management, considering land use and cover specifics, and provide useful baselines for REDD+ activities in countries with similar ecosystems.

Urban tree canopies drive human heat stress mitigation

Climate warming and urbanisation compound the public health risk posed by heat. Heat can be mitigated at local scales through urban greening, which provides shade and reduces surface and air temperatures. Yet, the relative effectiveness of different greening options on human thermal comfort based on physiology-based indices is understudied. We installed microclimate stations at 17 locations covering a gradient of tree canopy cover and perviousness in the city of Ghent, Belgium, and monitored the modified Physiologically Equivalent Temperature (mPET) during 195 days over Spring and Summer. We assessed the canopy cover, pervious surface fraction and building sky fraction based on field measures and hemispherical pictures. Unpaved locations with trees experienced a 2.4-fold reduction in the number of days with strong heat stress (mPET > 35 °C) compared to paved, treeless locations. Based on mixed models and our selected environmental variables, cooling effects were predominantly driven by tree canopy cover, where locations with 100% canopy cover had temperature maxima 5.5 °C mPET lower than treeless locations throughout the monitoring period. When air temperatures rose to 40 °C, cooling by tree canopies increased to 8.8 °C mPET. The pervious surface fraction and building view factor were less influential, generating variation of at most 1.7 °C and 1.1 °C mPET, respectively. In contrast, night-time temperatures were rather determined by the regional-scale urban heat island effect than by aforementioned local factors. Still, tree canopies slightly cooled the warmest nights only, whereas the vicinity of buildings led up to 1.2 °C mPET warming on average. Expanding the urban tree cover may therefore be the best solution for improving local thermal comfort levels when daytime heat peaks, but will provide little relief at night.

Tree species richness around urban red maples reduces pest density but does not enhance biological control

Urban trees often host greater insect pest abundance than trees in rural forests. This may be due, in part, to differences in tree diversity and canopy cover between these settings. Urban trees are often planted in isolation or monoculture, which favors pest accumulation. Gloomy scale, Melanaspis tenebricosa Comstock, is a pest of urban red maples (Acer rubrum L.) that is abundant where impervious surfaces dominate the local landscape. Increasing tree diversity and canopy cover around urban red maples may reduce gloomy scale abundance by supporting natural enemy communities. We investigated the effect that surrounding tree species richness and tree canopy cover had on gloomy scale abundance, natural enemy abundance, and biological control in red maple trees in Raleigh, NC, USA. We collected scales and natural enemies from red maples that spanned a gradient of tree species richness, canopy cover, and impervious surface values. We also measured gloomy scale parasitism and predation of sentinel prey in red maple canopies. Greater tree species richness and canopy cover were associated with lower gloomy scale density. Red maples in diverse settings also hosted fewer scales per natural enemy. Parasitoids were less common in maples in diverse settings, but generalist predator abundance was unaffected by tree diversity. Finally, tree species richness and canopy cover did not increase biological control of scales or sentinel prey. Our findings suggest that higher tree diversity and greater canopy cover may reduce gloomy scale density, but this is not entirely explained by the effects of natural enemies and biological control.

Factors affecting overwintering retreat-site selection in reptiles in an agricultural landscape

ContextUnderstanding what characteristics influence retreat-site selection by fauna is critical for both habitat management and species conservation. Despite the documented ecological values of surface rocks, there is limited knowledge of the attributes of surface rock that contribute to their use in agricultural landscapes or during winter months when reptiles are brumating, activity patterns are reduced, and sheltering individuals are most vulnerable to disturbance.ObjectivesWe surveyed reptiles sheltering beneath surface rocks in grazing farms in south-eastern Australia to address two questions: (i) What landscape factors influence the occurrence of reptiles over austral winter? (ii) What physical and thermal factors influence retreat-site selection?MethodsWe surveyed 14 sites, with three plots per site, stratified across a gradient of canopy cover. We measured landscape attributes of surveyed sites and thermal and physical characteristics of individual surface rocks to quantify relationships between the occurrence of reptiles in the landscape and the properties of retreats selected.ResultsWe found that relatively small patches of surface rock can support high reptile numbers, with density estimates up to of 208 individuals per hectare. Reptile abundance was positively associated with increased elevation and limited canopy cover. Reptiles selected smaller rocks with high surface area to volume ratio, were minimally embedded in the soil, and rocks supporting few invertebrates.ConclusionsConserving cryptozoic reptiles in agricultural landscapes can be enhanced through the appropriate management and retention of surface rock. We discuss implications for reptile conservation and surface rock management in agricultural landscapes.

Use of aerial distance sampling to estimate abundance of tule elk across a gradient of canopy cover and comparison to a concurrent fecal DNA spatial capture-recapture survey

Historically, aerial surveys have been used widely to monitor abundance of large mammals in the western United States. In California, such surveys have typically served as minimum count indices rather than true abundance estimates. Here, we evaluated the utility of aerial multiple covariate distance sampling (MCDS) to estimate abundance of three populations of tule elk (Cervus canadensis nannodes) in northern California. We also compared estimates and costs with published results from a concurrent fecal DNA spatial capture-recapture (SCR) survey. During December 2018 and 2019, we flew line transects for distance sampling of tule elk in Colusa and Lake counties. We modeled detection functions and evaluated effects of group size, canopy cover, and survey year. We averaged the top models comprising ≥0.95 of Akaike Model Weight and estimated abundance of both total and discrete populations. Detection probability increased with increasing group size and decreasing canopy cover. We estimated a two-year average total population size of N̂ = 674 elk (90% CI = 501–907) in our survey area which was similar to N̂ = 653 elk (90% CI = 573–745) from SCR estimates. Overall precision was greater (CV = 0.08; range = 0.11–0.30 by population) for SCR than for MCDS (CV = 0.18; range = 0.22–0.43 by population). Although estimates differed somewhat between methods for the individual populations, the combined estimate across the study region compared favorably. Total cost of SCR and MCDS surveys was $98,326 and $147,324, respectively. While SCR efforts were more precise and less expensive overall, our MCDS approach reduced staff time by 64% (587 person-hours) and the number of survey days by 87% (64 days). Our results suggest MCDS methods can produce reliable abundance estimates across a gradient of canopy cover, particularly when observations can be pooled across populations to decrease variance. We recommend future research to assess use of hybrid models, such as mark-recapture distance sampling or hierarchical distance sampling, to improve precision and estimation of detection probability.

Effects and response of the Cerrado ground-layer to frost along the canopy cover gradient.

Frost effects on savanna plant communities have been considered as analogous to those from fire, both changing community structure and filtering species composition. However, while frost impacts have been well-studied for the woody component of savannas, it is still poorly explored for the ground-layer community. Here, we investigated effects of frost in the Cerrado along a gradient of tree cover, focusing on ground-layer plant species, near the southern limit of the Cerrado in Brazil. We aimed to elucidate if the pattern already described for the tree layer also extends to the ground layer in terms of mimicking the effects of fire on vegetation structure and composition. We assessed how damage severity differs across species and across the tree-cover gradient, and we examined the recovery process after frost in terms of richness and community structure along the canopy cover gradient. Frost caused immediate and widespread dieback of the perennial ground-layer, with greatest impact on community structure where tree cover was lowest. However, frost did not reduce the number of species, indicating community resilience to this natural disturbance. Although frost mimicked the effects of fire in some ways, in other ways it differed substantially from fire. Unlike fire, frost increases litter cover and decreases the proportion of bare soil, likely hindering crucial processes for recovery of plant populations, such as seed dispersal, seed germination and plant resprouting. This finding calls attention to the risk of misguided conclusions when the ground layer is neglected in ecological studies of tropical savannas and grasslands.

Effects of canopy cover on fruiting intensity and fruit removal of a tropical invasive weed

Lantana camara (hereafter, Lantana) is among the worst invasive alien plants spread extensively across Africa, Australia and Asia at an alarming rate, posing significant challenges to conservation of native biodiversity. While, Lantana invasion is widely recognised to be more pronounced in open-canopy habitats (including deciduous forests, forest edges and gaps), the potential role of variation in seed dispersal across habitats varying in overstory canopy cover is poorly understood.Avian frugivores are among primary seed dispersers of the fleshy-fruited Lantana. We monitored 45 Lantana shrubs across a gradient of overstory canopy cover to determine the relationship between fruiting intensity and canopy cover. We watched 80 Lantana shrubs (240 h) across a canopy cover gradient to determine 1) differences in frugivore assemblage visiting Lantana across open- and closed-canopy habitats, 2) drivers of frugivore visitation on Lantana, and 3) relationship between seed disperser visitation rate and overstory canopy cover. We found that Lantana shrubs under low overstory canopy cover had higher fruit abundance than those in high canopy cover. Frugivore assemblage differed between Lantana shrubs in open- versus closed-canopy cover habitats. Drivers of frugivore visitation on Lantana varied across different frugivore species with a greater probability of occurrence of bulbuls (the primary seed dispersers of Lantana) on shrubs under low overstory canopy cover.Visitation rates of the effective seed dispersers were higher on shrubs under low overstory canopy cover. Thus, there was greater chances of dispersal of seeds in habitats with low overstory canopy cover.The study demonstrates variable fruiting intensity and fruit removal rate as a driver of differences in dispersal of seeds across habitats. It highlights greater vulnerability of open habitats to invasion and the need to prioritise Lantana management efforts in open habitats. Anthropogenic activities that lead to canopy openings (e.g. tree lopping and logging) likely facilitate Lantana invasion through greater fruit production and seed dispersal.

Moderate pine cover maximizes 10-year survival and growth in late-successional species of contrasting functional strategies

Monospecific pine forests are widespread due to extensive afforestation efforts and natural colonization of abandoned croplands in the Mediterranean Basin. It was originally thought that pines would facilitate the natural colonization of native late-successional resprouter species (e.g., hardwoods), but these species can be compromised if competition with pines outweighs their facilitative effect on these hardwood species. Managing the density or canopy cover of these widespread pine forests can potentially provide some “optimum” balance between facilitation and competition to maximize success in the introduction of late successional species while maintaining a tree stratum. We tested the response (survival and growth across 10 years) of six resprouter species covering a wide range of plant functional strategies, from drought-tolerant sclerophyllous shrubs and trees to malacophyllous drought-sensitive trees, across an experimental gradient of Aleppo pine canopy cover. Seedling performance varied according to the functional strategy, pine cover and time. High pine cover generally enhanced seedling survival, whereas moderate pine cover generally enhanced seedling growth, although this response was modulated by the functional strategy of the seedling species. Interactions between pines and seedlings were only detectable 2–3 years after plantation, increasing in intensity with time. The latter highlights the need of medium to long-term studies to evaluate plant-plant interactions in these water-limited environments with slow successional trajectories. Our results could be attributed to the shade tolerance of most of the introduced trees, combined with their low tolerance to the combination of high sunlight radiation and drought. We found an optimal pine cover of ca. 50% (equivalent to 300–400 trees/ha) in which both survival and growth of late successional species can be maximized, which help to select best locations for more efficient reforestation programs and set a threshold value to decide whether or not to perform tree thinning to enhance ecosystem diversity and, subsequently, resilience.

Variable seed bed microsite conditions and light influence germination in Australian winter annuals

Environmentally cued germination may play an important role in promoting coexistence in Mediterranean annual plant systems if it causes niche differentiation across heterogeneous microsite conditions. In this study, we tested how microsite conditions experienced by seeds in the field and light conditions in the laboratory influenced germination in 12 common annual plant species occurring in the understorey of the York gum-jam woodlands in southwest Western Australia. Specifically, we hypothesized that if germination promotes spatial niche differentiation, then we should observe species-specific germination responses to light. In addition, we hypothesized that species’ laboratory germination response may depend on the microsite conditions experienced by seeds while buried. We tested the laboratory germination response of seeds under diurnally fluctuating light and complete darkness, which were collected from microsites spanning local-scale environmental gradients known to influence community structure in this system. We found that seeds of 6 out of the 12 focal species exhibited significant positive germination responses to light, but that the magnitude of these responses varied greatly with the relative light requirement for germination ranging from 0.51 to 0.86 for these species. In addition, germination increased significantly across a gradient of canopy cover for two species, but we found little evidence to suggest that species’ relative light requirement for germination varied depending on seed bank microsite conditions. Our results suggest that variability in light availability may promote coexistence in this system and that the microsite conditions seeds experience in the intra-growing season period can further nuance species germination behaviour.

Shade tree canopy cover affects coffee plant traits across elevations in coffee farms in southwest Ethiopia

Coffee is an important crop in the global south. However, ongoing changes in the climate system reinforce the need to quantify coffee plants' ecological and eco‐physiological traits to assure coffee production in the future. One way to assess how environmental changes affect coffee performance is via leaf traits, most notably leaf carbon and nitrogen concentrations (to reflect the nutrient status), leaf stable carbon isotope composition (δ13C) to determine intrinsic water use efficiency (WUEi), and specific leaf area (SLA) to describe carbon gain relative to water loss within a plant canopy as these traits are related to yields. Therefore, we sampled coffee plants growing at contrasting elevations using a space‐for‐time substitution approach for warming and superimposed a canopy cover gradient to assess whether increasing canopy cover could modulate responses to temperature. Three coffee shrubs were sampled in each of 59 coffee farms in southwest Ethiopia across elevations of 1500–2160 m a.s.l. and along canopy cover gradients from open to deep shade. Soil nutrient concentrations, light availability, soil temperature and moisture were quantified for each coffee shrub. Elevation and shade tree canopy cover significantly and interactively affected WUEi. Elevation was found to be the driving factor for microclimate and soil factors which indirectly influenced both SLA and WUEi. Both of these coffee leaf traits are moderately governed by soil temperature whereas leaf N and C:N are mainly controlled by soil temperature and soil chemical variables. As elevation increased, WUEi kept increasing at light (< 35%) to intermediate shade levels (35–65%), and the values decreased at dense shade levels (65–100%) at high elevations, suggesting that coffee plants growing at high elevations with light shade can assimilate more CO2with minimum evaporative water loss. SLA declined with elevation. Leaf N and leaf C:N responded negatively and positively to shade canopy cover, respectively. In sum, elevation and canopy cover interactively determined microclimate and coffee leaf traits. Our findings are useful to adjust the intensity of shade, along with other tree‐level management tools, to modulate climate‐change effects on coffee at the farm level.

Local plant richness predicts bee abundance and diversity in a study of urban residential yards

Understanding the drivers of biodiversity in cities is a central goal of urban ecology. There is currently intense scientific and public interest in the factors that influence pollinator diversity in cities and their surroundings. Existing studies point to a variety of landscape and local factors as potentially important, including urbanization (often defined as impervious surface cover in the surrounding lands), tree canopy cover and the diversity and abundance of locally flowering plants. However, few studies have sought to weigh the relative importance of these predictors of bee community metrics. Using a set of 27 residential yards chosen to represent a gradient of both urbanization and tree canopy cover at a landscape scale, we used pan trapping and netting to assess the abundance and diversity of local bee communities across the City of Ottawa, Ontario, Canada. Surprisingly, the landscape factors (urbanization and tree cover) described only a tiny fraction (< 1%) of the total variance in bee abundance and diversity across sites. This was true regardless of the scale of analysis at which the landscape factors were measured. Instead, a yard's floral richness, and, to a somewhat lesser extent, its floral abundance, emerged as the most important predictors of a yard's bee community abundance and diversity. Our study offers an important counterpoint to a growing body of work emphasizing the impacts of landscape factors on bee communities. Instead, our research suggests that improving bee floral resources by increasing the plant species richness and abundance locally is a powerful tool to support bee conservation, regardless of the level of urbanization or tree cover in the surrounding landscape. Our work highlights that the practice of promoting ‘bee-friendly’ plantings in private yards, currently being undertaken by a number of non-profits around the world, can play an important role in restoring and maintaining urban pollinator communities.

Variation in characteristics and conservation values of plant communities on abandoned agricultural lands with and without fires

AbstractQuestionWhich plant community characteristics most consistently vary with prior land use?LocationOak Openings Preserve, Ohio, USA.MethodsIn 2020, we measured plant communities on 22 sites encompassing three prior land uses: (a) contemporary Quercus forests continuously forested since before the 1930s; (b) former agricultural lands, under cultivation in the 1930s and abandoned 70–80 years before our study and that were unburned; and (c) former agricultural lands also abandoned 70–80 years earlier and that were burned in 2013 prescribed fires. Among the three land uses, we compared 12 plant community variables, categorized into four groups characterizing different sets of community properties (structure, diversity, composition, and conservation values).ResultsA multivariate combination of the 12 community variables differed among all three land uses, each of the four categories of variables differed between at least two land uses, and eight of 12 individual variables differed between at least two land uses. Community structure displayed a gradient of decreasing tree canopy and understorey plant cover and increasing lichen–moss cover from continuously forested to unburned and burned formerly cultivated sites. Understorey plant species richness did not vary with land use, but species diversity was higher on cultivated sites, irrespective of fire history. While all three land uses now contain Quercus tree overstories, each land use exhibited unique understorey species composition. Only formerly cultivated sites contained state‐listed endangered species. Cultivated sites had a lower proportion of native species cover than did continuously forested sites, but native species still comprised over 90% of the plant cover on cultivated sites. Compared with continuous forests, the soil organic layer (O horizon) was five times thinner and loss on ignition in the 0–15 cm mineral soil 49% (unburned) and 66% (burned) lower on previously cultivated sites.ConclusionsCommunity characteristics varied in their sensitivity to land use history, with species composition among the most sensitive to prior land use. A dense sapling layer of Acer rubrum forming in long‐unburned Quercus forests across much of eastern North America was absent in our study on formerly cultivated sites, possibly due to dry, infertile soil. From a restoration and conservation standpoint of the study region's pre‐settlement, frequently burned and open savannas and woodlands, previously cultivated sites may be easier to keep open via prescribed fire. Moreover, perhaps precisely because much of the flora historically developed in open savannas and woodlands which previously cultivated sites on the contemporary landscape most closely mimicked, previously cultivated sites presently contain higher species diversity and more conservation priority species than do continuously forested sites.

Effect of environmental gradients on leaf morphological traits in the Fandoghlo forest region (NW Iran)

Abstract: The purpose of this study was to analyze the effects of altitude, the position of the trees along a gradient of canopy cover, and the orientation of their crown on leaf traits of 18 deciduous woody species belonging to 10 families in the Fandoglo forest region in Ardabil, North West of Iran. We measured eight leaf traits (leaf width, length, area, thickness, water content, leaf mass per area, specific leaf area, and dry matter concentration) of trees sampled at sites subjected to different light regimes (forest edge, forest understory, and isolated trees). All traits were measured on more than 3600 leaves from 90 trees sampled in two altitudinal ranges (low: 1300-1500 m a.s.l.; high: 1500-1700 m a.s.l.). A two-way ANOVA and t-test for independent samples were applied to test for differences in leaf traits between different altitudes and degree of canopy cover. The results confirmed that species’ leaf traits were more strongly correlated with the altitude and canopy cover rather than the orientation of the crown. No relationship between leaf traits and crown orientation was detected. All leaf traits had significantly higher values at low than at high elevation, indicating that environmental factors such as atmospheric CO2 concentration, temperature, light, irradiance, and wind deeply impact on foliar morphology and function; however, water content and specific leaf area showed an opposite trend. Also, species with different positions along the gradient of canopy cover could have different responses to elevation. Our results indicate that the variation of functional (morphological and physiological) traits in different tree species are affected by altitude and light regime. This might provide a theoretical basis for afforestation and forest management activities in the Fandoghlo forest region.

Shade alters savanna grass layer structure and function along a gradient of canopy cover

AbstractAimIn savannas, a grass‐dominated ground layer is key to ecosystem function via grass–fire feedbacks that maintain open ecosystems. With woody encroachment, tree density increases, thereby decreasing light in the ground layer and potentially altering ecosystem function. We investigated how light availability can filter individual grass species distributions and whether different functional traits are associated with response to a shade gradient in a landscape experiencing woody encroachment.LocationSavanna–forest mosaic in the Cerrado domain, southeastern Brazil.MethodsAlong an encroachment gradient of increasing tree leaf area index (LAI) and shade, we determined how changing light availability alters grass diversity and ground layer structure relative to grass cover and grass functional traits (photosynthetic pathway, underground storage organs, bud protection and traits related to grass shape, size and leaf dimensions).ResultsIncreasing shade led to a decrease in grass cover and grass species richness, and also compositional and functional changes. We found that where tree LAI reached 1, grass cover was reduced by 50% and species richness by 30%. While C4 grass species abundances decreased with increasing shade, the opposite pattern was true for C3 grasses. There were only small differences in light preferences among C4 subtypes, with phosphoenolpyruvate carboxykinase (PCK) species tolerating slightly more shaded conditions. Persistence of some C4 species under more shaded conditions was possible, likely due to an ability to store starch reserves via underground storage organs.ConclusionsWoody encroachment changes diversity and structure of the grassy layer that is critical to the functioning of savanna ecosystems, highlighting the dependence of the diverse grass layer on open and sunny conditions. Our results suggest a threshold of tree cover close to LAI ≈ 1 as being critical to cerrado grassy layer conservation.

Canopy openness affects microclimate and performance of underplanted trees in restoration of high-elevation tropical pasturelands

Restoration of abandoned, high-elevation pastures is needed across many ecosystems. Diverse abiotic and biotic stressors often limit establishment of native trees species, however, justifying the need for novel approaches to alleviate such stressors. Freezing damage often negatively impacts survival of planted trees across temperate landscapes and on some high-elevation tropical restoration sites, such as for Acacia koa (koa) in Hawaii, USA. Koa performs poorly under forest canopies, a potential limitation to the use of nurse trees for establishment on frost-prone sites. Using a heterogeneous canopy of a non-native conifer, Cryptomeria japonica, we underplanted koa seedlings along a simulated range of canopy shelter levels in combination with field fertilization. We tested the effect of a canopy cover gradient and nutrient availability on frost avoidance and tolerance responses, as well as the potential to harness koa's developmental plasticity to optimize growth and survival. C. japonica canopy cover provided protection from frost damage, with increased sheltering under greater canopy closure. When combined with fertilization, increasing canopy closure reduced frost damage and increased koa growth. Although we observed limited frost damage in our study, leaf-level soluble sugars increased during the winter and in more open microsites, reflecting a potential mechanism for frost tolerance in this tropical species. We conclude that frost-tolerant conifers used as nurse trees represent a potential tool to help establish native tree species on high-elevation, frost-prone sites.

Changes in conservation value from grasslands to savannas to forests: How a temperate canopy cover gradient affects butterfly community composition.

Temperate savannas and grasslands are globally threatened. In the Midwest United States of America (USA), for example, oak savannas persist today at a small percentage of recent historic coverage. Therefore, restoration of habitats of low and intermediate canopy cover is a landscape conservation priority that often emphasizes returning tree density to a savanna-like target value. Understanding how animal species react to such changes in vegetation structure is important for assessing the value of these restoration plans. We examined how butterfly community attributes in northwest Indiana USA, including community composition, richness, and abundance responded to a grassland-to-forest gradient of canopy cover. Butterfly community composition under intermediate canopy cover differed significantly from community composition in the most open or closed-canopy habitats. Composition of the plant community in flower was a significant predictor of three assessed attributes of the butterfly community—composition, richness, and abundance. Phenology, expressed as day-of-the-year, was also a strong predictor of these butterfly community attributes. Few butterfly species were habitat specialists as adults although canopy cover was a more important predictor of adult community composition than of richness or abundance of butterflies. Therefore, adult butterfly community differences along the canopy cover gradient were less about butterfly communities filled with habitat specialists for different canopy-defined habitats and more about gradual changes in community composition along this gradient. Overall, butterfly community richness was predicted to peak at about 34% canopy cover, butterfly abundance at about 53% canopy cover, community conservation value at about 59% canopy cover, and a combination of desirable conservation attributes–high diversity, high abundance, and high conservation value–was predicted to reach a peak of co-occurrence at about 67% canopy cover suggesting that habitats of intermediate canopy cover might be particularly effective for butterfly conservation in this region.

Long-term, fire-induced changes in habitat structure and microclimate affect Cerrado lizard communities

Fire transforms the structure of natural habitats and, consequently, modifies microclimates affecting ectotherm organisms that are particularly susceptible to changes in the thermal environment. Nevertheless, the effects of fire-induced microclimatic shifts upon natural populations have been neglected. We measured the central tendency and variation of habitat structural and microclimatic variables in experimental plots of Neotropical savanna vegetation subjected to different fire regimes and assessed their effects upon lizard community structure. In addition, we evaluated the underlying mechanisms linking fire-induced environmental changes to community structure, by comparing lizard body condition and survival between different fire regimes. Fire suppression promoted increased tree density, canopy cover and leaf-litter weight, whereas burning had the opposite effects, reducing the habitat structural complexity. The best predictors of fire regimes were means of structural variables, but variances of microclimatic variables, and the reduced structural complexity of burned plots both increased and decreased the variation of microclimatic variables. Lizard community structure was chiefly described by a gradient of decreasing tree density, canopy cover and leaf litter weight with increasing fire severity. About half of the lizard species were favored in the fire-protected plot, while the other half was favored in the burned plots, with most of the variation being explained by structural variables. Lizard body condition and survival rates were not affected by fire regimes, suggesting a dominant role of thermoregulation opportunities afforded by habitat structure—instead of food availability or predation rates—upon community structure. Our findings indicate that even sporadic fires can have profound effects upon lizard communities and that protecting some habitat patches from burning is essential to maximize lizard diversity in Cerrado landscapes.